Mr. Soros held put options linked to 7.1 million shares of SPY as of Dec. 31, compared to about 2.8 million shares at the end of the third quarter, according to a filing with the Securities and Exchange Commission. The value of that position jumped to $1.3 billion, up from $470 million, and made up about 11.1% of the fund’s holdings, by far the fund’s biggest position.

A put option grants the buyer the right to sell stock at a set price for a limited time. It generally rises in value as the price of underlying stock falls relative to the strike price.

Mr. Soros’s increased bearish bet came as the S&P 500 soared in the fourth quarter and finished the year up 30%. Stocks started 2014 on a sour note, with the S&P 500 tumbling 5.8% from mid-January through early February. The market has recovered in recent weeks and currently sits less than 1% off its all-time high.

It’s unclear whether Mr. Soros changed his position at any point this year as the most recent regulatory filing, published late Friday, accounted for positions reported during the final three months of 2013.

Overall in the fourth quarter, the value of Mr. Soros’s holdings rose to $11.8 billion from $9.1 billion in the third quarter.

Mr. Soros’s fund, which returned cash to outside investors last year, invests money for Mr. Soros and his family.

Investors who manage more than $100 million are required to disclose most securities holdings within a month and a half of the end of a quarter. The filings give the public a relatively fresh look at the portfolios of well-known investors. The fourth-quarter deadline was Friday.